The invention relates generally to computer numerical control and specifically to an apparatus for controlling the display of dot matrix characters on a cathode ray tube screen.
Because the information to be displayed with a computer numerical control is often of two of more types such as current machine status information and operator instruction information, it is desirable to display such information in different character fonts defining different character sizes and formats according to the way the types of information are to be used by the operator. For example, coordinate data for current axis positions should be readable from locations about the machine but removed from the control display so that an operator may perform manual machine positioning. On the other hand, it is satisfactory to display operator instruction data relating to speed overrides, part checking and the like so as to be readable only when standing relatively close to the control display.
The prior art has shown ways of producing characters of different formats in the same display by using a so-called pure video display wherein each character element corresponds to a phosphor dot of the display screen. This is quite cumbersome in that it requires that the state of the electron beam be defined for each and every phosphor dot individually.
Another scheme has been to mix dot matrix characters with pure video characters on the same display, but this is subject to the drawback of apparent wiggle between the two types of characters as well as requiring substantial storage to completely define the electron beam state for the pure video portion of the display.
Therefore, one object of this invention is to provide a video display controller capable of producing dot matrix characters of a plurality of fonts.
A further object of this invention is to generate characters of a plurality of fonts in such a way that their display on a cathode ray tube monitor shall be characterized by relative positional stability.
Other objects and advantages of the present invention shall be apparent from the following detailed description taken in conjunction with the drawings.